A security device that increases the number of design options available for a machine testable security feature formed in part from a light absorbing (e.g., magnetic) material, while more effectively hiding or concealing this material, is provided. The inventive security device achieves these results by physically separating this security feature from a visually detectable or public security feature. The security device comprises carrier substrates (12), (16) which are light-transmitting (transparent) substrates of a thickness from 4 to 26 microns, preferably colorless polymers. Also provided by way of this invention is a process for preparing the inventive security device as well as a security document that employs one or more such devices. (FIG.1)